This invention relates to a process for the preparation of resin-coated sands and molding shells, cores and the like casting molds prepared from such sands.
As is well known among those skilled in the art, resin-coated molding sands and shells, cores and the like molds prepared therefrom with use of organic resin binder(s) have been and are used broadly in the field of metal-casting technique. As an example, shell mold process, cold box process, hot box process and normal temperature hardenable mold process may be raised. The resin binders used in this engineering field must have high thermal strength so as to be durable even in contact with molten metal poured at the casting stage. Thus, higher heat resistant and thermally stable resin materials such as phenolic, furan-, urea- and/or urethane resin.
As the casting metal, iron and its alloys, cast steel, non-ferrous metals may be raised.
In the case of lower temperature casting metals such as aluminium and its alloys, the molds are not subjected to such a thermal history as enough to easily decompose mechanically the molds after casting for the recovery the contained sand for its reuse. In other words, the collapsability of the molds after casting is very poor, thus a large quantity of heat energy and labor must be consumed for the later sand separation and recovery.
In the case of pig iron castings, on the other hand, especially those for the production of automotive parts as an example, they are made as thinner as possible for the purpose of attaining lower fuel consumption rate of the vehicle. In addition, the whole design and configuration of these parts are becoming rather more complicated. These tendencies accelerate disadvantage of increased sand residual in the cast products. After all, labor cost for separation and cleaning of such residual sand from the castings is still increasing.
On the other hand, in the case of steel castings for which rather higher pouring temperature must be adopted, the residual strength of the molds is rather too much high, thus resulting in liable crack formation in the cast steel products. Therefore, the range of use of resin-coated sand molds has been rather limited.
Therefore, it will be seen that in the prior art there is a grave problem, which is very difficult to solve, such that the higher the thermal strength of the binders is to be met in the casting stage with the shell molds including these binders, so the collapsability of the molds would become lesser. Therefore, sand separation will require more energy and labor.